The invention relates to a drying machine, and more particularly to a hot air drying machine for drying clothes or the like.
Conventionally, in drying machines for the above described purpose, it has been a general practice to adjust the time required for drying clothes or the like by setting a suitable time control device, for example, a timer to a desired time, since such time for drying differs depending on the kinds and amount of materials to be dried and also on variations of room temperatures and power source voltage, which drying time, however, must inevitably be determined by experience and is consequently very uneconomical from the view point of efficiency and processing cost, sometimes resulting in damage to the materials to be dried due to over-drying or making it necessary to dry such materials again if the drying operation is stopped with the materials insufficiently dried due to the period of drying time set in advance being too short.
In order to overcome such disadvantages, there was conventionally been proposed a drying machine equipped with a control device for controlling the drying rate by detecting the relative difference of the exhaust air temperature and the ambient temperature for the drying machine through temperature sensing elements respectively. However, such a conventional drying maching still has such drawbacks that the drying operation is stopped before sufficient drying is achieved due to insufficient rates in temperature rise of exhaust air especially when the power source voltage varies, for example, when the power source voltage is high, thus adversely affecting the efficient drying operation and stable drying rates of the dried materials.
Furthermore, in such conventional drying machines with unstable drying rates mainly due to variations of power source voltage, it is almost impossible to complete the drying operation with the materials to be dried kept exactly in a predetermined damp condition in cases where such a degree of partial drying is desired depending on the requirements, for example, for subjecting the dried materials to subsequent processings in such accurately partially damp condition.